The assembly of an exhaust system normally includes the engine exhaust manifold and connected thereto a catalytic convertor and successively a muffler and tail pipe. In normal operation and with incomplete combustion there are chemical and other impurities in the exhaust gases passing through the exhaust manifold which are harmful to the catalytic convertors presently in use and which escape therethrough to atmosphere delivering harmful chemicals, gases and vapors thereto. Various efforts have been made to improve the quality of combustion and for cutting down upon contaminents within and passing through the exhaust manifold such by introduction of increased atmospheric air into the intake of the carburetor or the intake manifold of a vehicle in an effort to burn-off more efficiently some of the combustibles and to otherwise oxidize some of the harmful chemicals which may escape combustion in the combustion chamber which may normally pass through the exhaust manifold for application to conventional catalytic convertors.